First I will explain what a Seed or a Mnemonic phrase is?
Mnemonic phrase - It is a 12 or 24 letters word which will be generated when you create a wallet. You can store that in a paper, so that it can be used later to recover your funds if the device breaks down or not useful.
The "Passphrase" is an additional password used to secure your mnemonic seed. If your recovery seed is lost or hacked, then you will loose all your funds. In order to protect a seed of your wallet, passphrase is implemented. Even if your seed is stolen, it cannot be lost as it will have an additional feature Passphrase that protects your funds.
There are many wallets that support passphrase feature like Ledger Nano S, Trezor wallet, Exodus, Coinomi etc.
If a passphrase protection is disabled on your wallet, you can enable passphrase protection on your device. Unlock your device and check "Advanced" tab and you can enable passphrase there. A new wallet will be created inside your wallet, it will be like a
hidden wallet inside your wallet.
Hope this will help the newbies or those who have not enabled this feature on their device.
Also, I would like to know which wallet are you using? Do you have this feature on your device? Or
How do you protect your Seed?